This project seeks the site and mechanism of action of transretinal electrical current when used for stimulating the retina. Most experiments will use the toad Bufo marinus. A pair of intraretinal microelectrodes will selectively stimulate the different layers of the retina while another electrode records the activity of the terminal arborizations of retinal ganglion cells in the optic tectum. The site of action of the current should be the region with the lowest threshold. Intraretinal recording of the electroretinogram and intraretinal staining techniques will be used to locate the stimulating electrodes within the retina. This work will improve our understanding of retinal physiology and has possible application to the testing of patients with certain disorders of the eye.